CN115497786A

CN115497786A - X-ray tube anode with integrated collimator

Info

Publication number: CN115497786A
Application number: CN202210679272.3A
Authority: CN
Inventors: K·O·格陵兰
Original assignee: Moxtek Inc
Current assignee: Moxtek Inc
Priority date: 2021-06-17
Filing date: 2022-06-16
Publication date: 2022-12-20
Also published as: DE202022103282U9; DE202022103282U1; US20220406557A1

Abstract

The collimator of the X-ray tube may be a monolithic integrated structure. The collimator may include a proximal end closest to the cathode and a distal end furthest from the cathode. The proximal end may abut a vacuum inside the X-ray tube. The distal end may abut air. The collimator may include an aperture extending therethrough. An X-ray window may be mounted through the aperture. The aperture may include a collimation region between the X-ray window and the distal end, and a drift region between the X-ray window and the proximal end. The X-rays may be generated inside the collimator.

Description

X-ray tube anode with integrated collimator

Technical Field

The present invention generally relates to X-ray sources.

Background

A large voltage between the cathode and the anode of an X-ray tube (sometimes a heated filament) can cause electrons to be emitted from the cathode to the anode. The anode can include a target material. The target material may generate X-rays in response to electron impact from the cathode.

Disclosure of Invention

The X-ray tube may include a cathode and an anode electrically insulated from each other. The cathode can be configured to emit electrons toward the target material of the anode. The target material may be configured to emit X-rays from the X-ray tube in response to impinging electrons from the cathode.

The anode may comprise a collimator. The collimator (a) may be a monolithic, unitary structure, (b) may have an aperture extending therethrough, and (c) may be configured to collimate X-rays.

An X-ray window may be mounted through the aperture. The aperture may be aimed to emit X-rays through the aperture of the collimator, through the X-ray window, and out of the X-ray tube.

The collimator may include a proximal end closest to the cathode and a distal end furthest from the cathode. The proximal end may abut the vacuum inside the X-ray tube, while the distal end may abut air.

Brief description of the drawingsthe accompanying drawings (which are not necessarily to scale)

Fig. 1 is a cross-sectional side view of a transmission target X-ray tube 10 having a collimator 11. The proximal end 11p of the collimator 11 may abut a vacuum inside the X-ray tube 10. The distal end 11d of the collimator 11 may be exposed to air and may abut air. The aperture 14 of the collimator 11 may surround the target material 19 of the X-ray tube 10.

Fig. 2 is a cross-sectional side view of a reflective target X-ray tube 20 with a collimator 11. The proximal end 11p of the collimator 11 may abut a vacuum inside the X-ray tube 20. The distal end 11d of the collimator 11 may be exposed to air and may abut the air. The target 19 of the X-ray tube 20 may form part of the wall of the aperture 14 of the collimator 11.

Fig. 3 is a cross-sectional side view of a transmission target X-ray tube 30 similar to the transmission target X-ray tube 10. The diameter 17d of the collimation region 17 of the transmission target X-ray tube 30 increases with increasing distance from the X-ray window 16.

Fig. 4 is a cross-sectional side view of a reflective target X-ray tube 40 similar to the reflective target X-ray tube 20. The ring 31 surrounds the collimator 11 of the reflective target X-ray tube 40.

Fig. 5 is a cross-sectional side view of a reflective target X-ray tube 50 with a collimator 11. The proximal end 11p of the collimator 11 may abut a vacuum inside the X-ray tube 50. The distal end 11d of the collimator 11 may be exposed to air and may abut the air. A gap 52 exists between the collimator 11 and the target 19 of the X-ray tube 50.

Fig. 6 is a cross-sectional side view of a transmission target X-ray tube 60 having a collimator 61. A gap 52 exists between the collimator 61 and the target 19 of the X-ray tube 60.

Definition of

The following definitions, including plural forms thereof, apply throughout this application.

As used herein, the term "adhesive" includes any material that may be used to bond the X-ray window 16 to the collimator 11 and form a hermetic seal between the X-ray window and the collimator 11. Exemplary adhesives include glues, epoxies, polymers, solders, and brazes.

As used herein, the term "uniformly dispersed throughout" means dispersed completely uniformly, uniformly dispersed within normal manufacturing tolerances, or nearly completely uniformly dispersed such that any deviation from completely uniform dispersion has negligible effect on the general use of the device.

As used herein, "over," "located" and "over" mean directly over or over with some other solid material therebetween. The terms "directly on" and "adjacent" mean directly and immediately adjacent contact.

As used herein, the term "monolithic" refers to seamless and continuous. The monolithic structures herein have the same material composition throughout. For example, concrete walls formed at one time in a single casting step and a subsequent single curing step are of monolithic construction. As another example, a collimator formed at once from a single piece of material is of monolithic construction.

As used herein, the terms "integrally connected" and "integrated" mean that the integrally connected devices are formed together and continuous at the same time, with no seams or joints between them.

As used herein, the term "same material composition" means identical, identical or nearly identical within normal manufacturing tolerances, such that any deviation from identical is negligible for the normal use of the device.

As used herein, the term "X-ray tube" is not limited to tubular/cylindrical devices. The term "tube" is used because this is the standard term for X-ray emitting devices.

Detailed Description

X-ray tubes can be used for material analysis (XRD and XRF), static dissipation, non-destructive inspection of material thickness, imaging, and backscatter imaging. Desirable X-ray tube characteristics include being small, lightweight, inexpensive, alignment of components during manufacture, fewer components to facilitate manufacture, and the ability to block X-rays emitted in undesired directions. The present invention includes an X-ray tube with a collimator 11 to meet these needs. Each example may satisfy one, some, or all of these requirements.

As shown in fig. 1-6,

X-ray tubes

10, 20, 30, 40, 50 and 60 are shown to include a cathode 12 and an anode 22 that are electrically isolated from one another. For example, the cathode 12 and the anode 22 may be electrically insulated from each other by the electrical insulation means 13. The electrical insulation means 13 may be a cylinder or a disc. The electrically insulating means 13 may be made of glass or ceramic. The anode 22 may be stationary.

The cathode 12 may be configured to emit electrons 15 toward the target material 19 of the anode 22. For example, the cathode 12 may include an electron emitter 12e, such as a filament, that will emit electrons 15 due to high temperature and large voltage differences. The target material 19 may be configured (e.g., by selecting the material) to emit X-rays 21 from the

X-ray tubes

10, 20, and 30 in response to impinging electrons 15 from the cathode 12.

As shown in fig. 1-5, the

X-ray tubes

10, 20, 30, 40 and 50 include a collimator 11 for collimating X-rays 21. The collimator 11 may be a single collimator (only one collimator in the X-ray tube). The use of a single collimator may reduce the number of components, thereby simplifying manufacturing.

The collimator 11 may have a proximal end 11p closest to the cathode 12 and a distal end 11d furthest from the cathode 12. The proximal end 11p may abut a vacuum inside the

X-ray tubes

10, 20, 30, 40 and 50. The distal end 11d may be exposed to air and may abut air outside the

X-ray tubes

10, 20, 30, 40, and 50. The vacuum may be inside the electrical insulation means 13. The distal end 11d may extend outwardly from the

X-ray tubes

10, 20, 30, 40 and 50 as the most protruding means at the X-ray emitting end of the

X-ray tubes

10, 20, 30, 40 and 50. The collimator 11 may adjoin the electrical insulation 13 at one end and may be located outside the

X-ray tubes

10, 20, 30, 40 and 50 at the other end.

The collimator 11 may be a one-piece integrated structure. The monolithic integrated structure of the collimator 11 may have a continuous and uninterrupted heat flow path to improve heat transfer characteristics. Furthermore, the monolithic integrated structure of the collimator 11 may have a continuous and uninterrupted energizing path to avoid contact resistance and allow a uniform current density through the collimator 11. The aperture 14 may extend through the core of the collimator 11. The aperture 14 may be aimed to allow X-rays 21 to be emitted from the

X-ray tubes

10, 20, 30, 40 and 50.

An X-ray window 16 may be mounted through the aperture 14. An X-ray window 16 may be mounted inside the aperture 14. The X-ray window 16 may form a gas-tight seal with the collimator 11. The X-ray window 16 may separate the vacuum from air. The X-ray window 16 may include some or all of the characteristics of an X-ray window described in U.S. patent No. US 9,502,206 (e.g., low deflection, high X-ray transmission, low visible and infrared light transmission), the entire contents of which are incorporated herein by reference.

In one aspect, the anode 22 may consist essentially of the collimator 11, the X-ray window 16, the binder, and the target material 19. An adhesive may be used for mounting the X-ray window 16 to the collimator 11 and for mounting the collimator 11 to the electrically insulating means 13. In another aspect, the anode 22 can consist essentially of the collimator 11, the X-ray window 16, the binder, the target material 19, and the ring 31 (described below). An adhesive may be used for mounting the X-ray window 16 to the collimator 11, for mounting the collimator 11 to the ring 31 and for mounting the ring 31 to the electrically insulating device 13. At least 70%, at least 80%, at least 85%, at least 90%, or at least 95% by weight of anode 22 may be collimator 11.

The aperture 14 may include (a) a collimation region 17 between the X-ray window 16 and the distal end 11d, and (b) a drift region 18 between the X-ray window 16 and the proximal end 11 p.

Some or all of the collimators 11 surrounding the collimation areas 17 may protrude outwards at the X-ray emitting end of the

X-ray tube

10, 20, 30, 40 or 50 as solid objects protruding furthest. For example, 20%,. Gtoreq.50%,. Gtoreq.75%,. Gtoreq.95% or all of the collimators 11 surrounding the collimation area 17 may protrude outwards from any other solid part of the X-ray tube.

The design of each X-ray tube may have a relationship between the length 17L of the collimation region 17 and the length 18L of the drift region 18. The length 17L of the collimation area 17 is measured as the shortest length between the X-ray window 16 and the distal end 11d. The length 18L of the drift region 18 is measured as the shortest length between the X-ray window 16 and the proximal end 11 p.

A shorter length 17L of the collimation area 17 is preferred for increasing the X-ray flux and reducing the material of the collimator; however, for a narrower X-ray beam, it is preferable that the length 17L of the collimating region 17 is longer.

A shorter length 18L of the drift region 18 is preferred to reduce the likelihood of arcing and to reduce the material of the collimator 17. A longer length 18L of the drift region 18 is preferred for increased X-ray shielding and reduced electron backscattering to the electrically insulating means 13.

Example relationships between the length 17L of the collimating region 17 and the length 18L of the drift region 18 include: 0.2 to 18L/17L, 0.5 to 18L/17L or 1 to 18L/17L. Other examples include: 18L/17L is less than or equal to 1, 18L/17L is less than or equal to 1.3 or 18L/17L is less than or equal to 1.6.

The relationship between the length 17L of the collimating region 17 and the diameter 17d of the collimating region 17 can be chosen to balance between better collimation of the X-ray beam and reduction of material weight and cost. For example, 0.5. Ltoreq.17L/17 d, 1. Ltoreq.17L/17 d or 1.4. Ltoreq.17L/17 d. Other examples include 17L/17d ≦ 1.4, 17L/17d ≦ 3, or 17L/17d ≦ 5. The diameter 17d is measured perpendicular to the longitudinal axis of the X-ray tube.

The relation between the diameter 17d of the collimation region 17, the diameter 16d of the X-ray window 16 and the diameter 18d of the drift region 18 may be selected to improve the manufacturability and collimation of the X-rays 21. For example, 17d 16d 18d. Each diameter is measured perpendicular to the longitudinal axis of the X-ray tube. If the device has different diameters in different directions, the relationship will select the largest of these diameters.

Using the collimator 11 as described herein, the x-ray window 16 may extend beyond the electrically insulating means 13, closer to the sample. For example, the X-ray window 16 may be positioned ≧ 0.5mm, ≧ 2mm or ≧ 4mm beyond the most distal end of the electrically insulating means 13, measured parallel to the longitudinal axis of the X-ray tube. The longitudinal axis of the X-ray tube may extend from the electron emitter 12e to the target 19 at the anode 22 (i.e., parallel to the electron beam 15).

The proximal end 11p of the collimator 11 abuts the vacuum inside the

X-ray tubes

10, 20, 30, 40 and 50. In contrast, in the X-ray tube 60, the proximal end 61p of the collimator 61 does not abut on the vacuum. The proximal end 61p instead abuts the material 63, which material 63 may be solid or liquid. The material 63 may span the gap 52 between the collimator 61 and the anode 22. The material 63 may surround the collimator 61 and enclose the proximal end 61p of the collimator 61.

As shown in the transmission

target X-ray tubes

10 and 30 of fig. 1 and 3, the target material 19 can be located on the X-ray window 16. The target material 19 may adjoin the X-ray window 16. The aperture 14 of the collimator 11 may surround the target material 19. The orifice 14 may be aimed (a) to transmit electrons 15 from the electron emitter 12e through the drift region 18 to hit the target material 19; and (b) to transmit the generated X-rays 21 through the collimation region 17 and out of the

X-ray tube

10 or 30.

As shown in the reflective

target X-ray tubes

20 and 40 in fig. 2 and 4, the target material 19 may (i) be separate from the X-ray window 16, (ii) be inside the collimator 11, and (iii) form part of the wall of the aperture 14. The orifice 14 may be aimed (a) to transmit electrons 15 from the electron emitter 12e through the drift region 18 to hit the target material 19; and (b) to transmit the generated X-rays 21 through the collimation region 17 and out of the

X-ray tube

20 or 40.

A transmission target X-ray tube 30 is shown in fig. 3. The X-ray tube 30 may have the characteristics as described above for the X-ray tube 10. However, the shape of the collimation areas 17 of the

X-ray tubes

10 and 30 is different.

In the transmission target X-ray tube 30, the diameter 17d of the collimation area 17 increases with increasing distance from the X-ray window 16. The collimating area 17 may have a truncated cone shape. The truncated cone shape may have a narrower diameter 17d closer to the X-ray window 16 and a wider diameter 17d closer to the distal end 11d.

The angle 17a of the walls of the collimating area 17 may be directed towards the electron focus at the target 19. Example angles 17a of the walls of the collimating region 17 include at least 20 °, 30 °, or 40 °; and not more than 50 °, 60 °, 70 °, or 80 °. The angle can be measured between a line 35 aligned with the wall of the collimation area 17 and the face of the X-ray window 16.

Such a shape of the collimation area 17 may improve the shape of the X-ray beam. Without the truncated cone shape, the X-rays may pass through the corner of the distal end 11d of the collimator 11. Some of these X-rays are attenuated and the overall X-ray beam profile obtained is undesirable.

Shown in fig. 4 is a reflective target X-ray tube 40. The X-ray tube 40 may have the characteristics as described above for the X-ray tube 20.

The

X-ray tubes

30 and 40 may further comprise a ring 31 surrounding the collimator 11. Due to the difference in thermal expansion coefficient between the collimator 11 and the electrically insulating means 13, the electrically insulating means 13 may crack when the two components are sealed (e.g. brazed) together. The addition of the ring 31 solves this cracking problem.

The ring 31 may be located between the collimator 11 and the electrically insulating means 13. The ring 31 may be attached to the collimator 11 and the electrically insulating means 13.

As shown in fig. 3, there may be a gas-tight seal 33 (first gas-tight seal) between the ring 31 and the collimator 11. There may be a hermetic seal 33 (second hermetic seal) between the ring 31 and the electrically insulating means 13. The hermetic seal 33 may be an adhesive, such as a brazed joint.

It is noted that in fig. 3 there is no such gas-tight seal 33 between the collimator 11 and the electrically insulating means 13. They are also not directly hermetically sealed to each other. Since there is no direct hermetic seal 33 in this position, the collimator 11 and the electrically insulating means 13 expand and contract at different rates during heating and cooling, so that they can slide past each other.

As shown in fig. 3, the outer surface of the ring 31 may further comprise a channel 32 surrounding the ring 31. The channel 32 may allow the ring 31 to flex, thereby further reducing stress in the electrical insulation means 13.

The coefficient of thermal expansion of the ring 31 is similar to the coefficient of thermal expansion of the electrically insulating means 13. The ring 31 may store stress during heating and cooling. Without the ring 31, this stress would be stored in the electrically insulating means 13. The ring 31 may be made of a material that is more ductile than the electrical insulation means 13 and is able to better store such stresses without breaking. The ring 31 may be made of metal.

The collimator 11 and the ring 31 in the

X-ray tubes

30 and 40 may have the following material composition. The collimator 11 may comprise tungsten. The collimator 11 may comprise at least 50, 75, 90 or 95 weight percent tungsten.

Ring 31 may comprise cobalt, nickel and iron. The ring 31 may be made of Kovar (Kovar). Ring 31 may comprise at least 50, 75, 90, or 95 weight percent of a combination of iron, nickel, and cobalt. Ring 31 may comprise at least 50 weight percent iron, at least 20 weight percent nickel, and at least 10 weight percent cobalt.

Although the hermetic seal 33 and the passage 32 are not shown in fig. 4, these features are also applicable to the X-ray tube 40. The ring 31 and hermetic seal 33 of the

X-ray tubes

30 and 40 are suitable for any of the other X-ray tubes described herein.

As shown in the reflective target X-ray tube 50 in fig. 5, the target material 19 may be spaced apart from the X-ray window 16 and outside the collimator 11. The aperture 14 can be aimed to transmit X-rays 21 from the target material 19 through the drift region 18, through the collimation region 17, and out of the X-ray tube 10.

Because less shielding is required by integrating the collimator 11 with the rest of the anode 22, the

X-ray tubes

10, 20, 30 and 40 can be made relatively small and light. The X-rays are generated inside the collimator 11. The target material 19 is located inside the aperture 14 between the proximal end 11p and the distal end 11d of the collimator 11. Because the target material 19 is located inside the collimator 11, shielding from stray X-rays is improved.

In contrast, in the

X-ray tubes

50 and 60, there is a gap 52 between the collimator 11 and the target 19. In these

X-ray tubes

50 and 60, it may be more difficult to shield stray X-rays 21. Thus, the

X-ray tubes

50 and 60 may be larger and heavier than the

X-ray tubes

10, 20, 30 and 40. Further, there is a greater risk of X-ray leakage in the

X-ray tubes

50 and 60.

The

X-ray tubes

10, 20, 30 and 40 are superior to the

X-ray tubes

50 and 60. The X-ray tube 50 is preferred over the X-ray tube 60.

The monolithic and integrated collimator 11 described herein may improve manufacturability of the

X-ray tubes

10, 20, 30, 40, and 50 because (a) fewer components simplify the manufacturing process, and (b) fewer components minimize stacking tolerances, thus producing a more accurate final product.

In one example collimator 11, 18l =7.2mm,17l =6.8mm,17d =4.8mm, and 18d =2.8mm.18L, 17L and 17d are as defined above. 18d is the diameter of drift region 18. In this example, the outer diameter of the collimator across most of the drift region 18 and across the collimation region 17 is 8.5mm.

The

collimators

11 and 61 may be made of a material having a high melting point and having the ability to block X-rays. The following materials/chemical elements may be uniformly dispersed in the collimator 11 or 61: at least one element in the

collimator

11 or 61 has an atomic number 42 or 74. At least 80 weight percent of the elements in the

collimator

11 or 61 have an atomic number 42 or 74. The

collimator

11 or 61 may comprise 60 or more, 70 or more or 85 or more percent by weight of tungsten, molybdenum or silver. In addition to tungsten, molybdenum or silver, the

collimator

11 or 61 may include copper, nickel and iron, lanthanum and oxygen, rhenium, or combinations thereof. The

collimator

11 or 61 may comprise more than or equal to 10% and less than or equal to 35% by weight of copper.

The

collimators

11 and 61 described herein may be manufactured by machining.

Claims

1. An X-ray tube comprising:

a cathode and an anode electrically insulated from each other, the cathode configured to emit electrons to a target material of the anode, and the target material configured to emit X-rays from the X-ray tube in response to impinging electrons from the cathode;

a collimator that (a) is a monolithic integrated structure, (b) has an aperture extending therethrough, and (c) is configured to collimate the X-rays;

an X-ray window mounted through the aperture, the aperture configured to be aimed such that the X-rays are emitted through the aperture, through the X-ray window, and out of the X-ray tube; and the collimator includes a proximal end closest to the cathode and a distal end farthest from the cathode, the proximal end abutting a vacuum inside the X-ray tube, the distal end abutting air.

2. The X-ray tube of claim 1, wherein the aperture comprises a collimation region between the X-ray window and the distal end, and the collimation region has a truncated cone shape with a narrower diameter near the X-ray window and a wider diameter near the distal end.

3. The X-ray tube of claim 1, further comprising:

an electrical insulation device attached to and electrically insulating the anode from the cathode;

a ring surrounding the collimator;

said ring being hermetically sealed to said collimator and to said electrical insulation means; and the collimator and the electrically insulating means are not directly hermetically sealed to each other.

4. The X-ray tube of claim 3, wherein at least 75% by weight of the collimator is tungsten and at least 75% by weight of the ring is cobalt, nickel and iron.

5. The X-ray tube of claim 1, wherein the X-rays are generated inside the collimator.

6. The X-ray tube of claim 1, wherein the collimator is part of the anode and at least 80% of the anode by weight is the collimator.

7. The X-ray tube of claim 1, wherein the X-ray window is mounted within the aperture.

8. The X-ray tube of claim 1, wherein:

the aperture comprises a collimation region between the X-ray window and the distal end;

the aperture comprises a drift region between the X-ray window and the proximal end; and

the diameter of the collimation region is larger than the diameter of the X-ray window, and the diameter of the X-ray window is larger than the diameter of the drift region, each diameter measured perpendicular to the longitudinal axis of the X-ray tube.

9. The X-ray tube of claim 1, wherein the target material is located inside the aperture between the proximal and distal ends of the collimator.

10. The X-ray tube of claim 1, wherein the target material forms a portion of a wall of the orifice.